G. M. Poletaev

Contributions of different mechanisms of self-diffusion in face-centered cubic metals under equilibrium conditions

The contributions of different mechanisms of self-diffusion in face-centered cubic metals Ni, Cu, and Al at thermodynamic equilibrium have been analyzed using the molecular dynamics method. The vacancy, divacancy, and cyclic mechanisms of self-diffusion, as well as the mechanisms involving the vacancy migration to the second coordination sphere and the formation and recombination of Frenkel pairs, have been considered. It has been shown that the second in contribution to the self-diffusion after the vacancy mechanism in the metals under consideration is the migration of divacancies. The third is the mechanism involving the formation and recombination of dynamic Frenkel pairs. The cyclic mechanisms (with simultaneous atomic displacements) and the vacancy migration directly to the second coordination sphere in face-centered cubic metals are unlikely.

Structural transformations of stacking fault tetrahedra upon the absorption of point defects

Mechanisms of the structural modification of stacking fault tetrahedra (SFTs) upon the absorption of point defects have been studied by the method of molecular dynamics. The sequential absorption of vacancies by a perfect SFT is accompanied by the following transformations: (i) the formation of a step on one of the SFT faces, (ii) a change in the step sign upon reaching the middle of the face, (iii) the formation of an SFT with truncated vertex, and (iv) the formation of the perfect SFT. Upon the absorption of interstitial atoms, the stages of SFT transformation follow the reverse order.

Molecular dynamics investigation of the diffusion permeability of triple junctions of tilt and mixed-type boundaries in nickel

The diffusion permeability of triple junctions of high-angle tilt boundaries 〈111〉 and 〈100〉 and mixed-type boundaries in nickel has been investigated using the molecular dynamics method. It has been shown that the diffusion permeability of equilibrium triple junctions does not exceed the permeability of the grain boundaries forming them. The effective diffusion radius of the considered triple junctions and the width of the grain boundaries are determined.

Dynamic collective displacements of atoms in metals and their role in the vacancy mechanism of diffusion

The phenomenon of dynamic collective displacements of atoms in face-centered cubic crystals has been revealed using molecular dynamics method. This phenomenon plays an important role in the vacancy mechanism of diffusion. The vacancy mechanism is provided by the collision of two regions of collective atomic displacements that move a migrating atom and a vacancy toward each other. The collective thermal atomic displacements from crystal lattice sites occur as a result of the nonuniform momentum distribution of atoms according to the Maxwellian distribution. Owing to their statistical nature, the degree of correlation of the atomic displacements depends neither on the temperature nor on the interatomic interaction potential.

Mutual diffusion at the interface in a two-dimensional Ni-Al system

Mutual diffusion at the interface in a two-dimensional Ni-Al system has been studied by the method of molecular dynamics. It is established that the main diffusion mechanism consists in correlated jumps of atoms over the vacancies near misfit dislocation cores.

Mechanisms of grain-boundary diffusion in two-dimensional metals

The mechanisms of diffusion via grain boundaries in two-dimensional metals have been studied by method of molecular dynamics. It is established that the diffusion can proceed by two mechanisms, which results in deviations from the Arrhenius law. The first mechanism is related to the formation of chains of atomic displacements between two dislocation cores along the boundary (for high-angle boundaries, between the regions of contraction and extension); the second mechanism consists in a cyclic exchange of atomic sites near the same dislocation core (for high-angle boundaries, near the defect region).

Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metals

Abstract The study of diffusion of hydrogen atoms in the crystal lattice of fcc metals Pd, Ni, Al, Ag was performed by the method of molecular dynamics. The diffusion characteristics of hydrogen impurity (activation energy of hydrogen atom migration and pre-exponential factor in the Arrhenius equation) in the considered metals were calculated. It is shown that the prevailing mechanism of the over-barrier hydrogen diffusion in fcc metals consists of successive migration through octahedral and tetrahedral pores. During migration, as a rule, the hydrogen atom is not delayed in tetrahedral pores.

Diffusion Mechanisms near Tilt Grain Boundaries in Ni3Al Intermetallide

The paper is devoted to the research of diffusion mechanism in Ni3Al intermetallide over grain boundaries of tilt <111> and <100> by the method of molecular dynamics. It was found that grain boundary diffusion represented the combination of three main mechanisms: migration of atoms along the nuclei of grain boundary dislocations, cyclic mechanism near the nuclei and the formation of the chain of displaced atoms from one nucleus of dislocation to the nucleus of the other one. Diffusion mobility of Ni atoms was essentially bigger than the mobility of Al atoms. Grain boundary slipping and intergrain slipping were also observed during the deformation of the bicrystal.

The study of the thermal stability of Ni3Al nanoneedles using computer simulation

The study of the thermal stability of Ni3Al nanoneedles in the dependence on the sharpness and crystallography orientation of the needle axis was held using molecular dynamics method. It is shown that the most stability nanoneedles in the conditions of thermal influence are the nanoneedles with the axis along [111] direction. Violation of the nanoneedles stability associated with their blunting, which is caused by surface diffusion. Stable radius of curvature of the needles depends on the angle of the tip and orientation of the needle axis. It is 0.6-1 nm at low temperatures.

The formation of excess free volume in triple junctions of and tilt boundaries in Ni at crystallization

The formation of excess free volume in triple junctions of and tilt boundaries in Ni at crystallization was studied by the method of molecular dynamics. It is shown that the triple junctions, containing excess free volume, mainly forms during crystallization process in the result of “locking” of the liquid phase density at a meeting of the three crystallization fronts and, as a consequence, of the concentration of excess free volume in the triple junction after solidification. The calculation of excess free volume formed in the triple junctions during crystallization was carried out. The peculiarities of formation of the free volume in the triple junctions of low and large-angle and tilt boundaries were studied using molecular dynamics simulations. It is shown that the main part of the free volume is accumulated during crystallization in the area of the grain boundaries and the triple junctions.